1. Field of the Invention
The present invention relates to analytical electron microscope applications, and more particularly to a method and apparatus for cleaning a specimen stage and specimen for viewing in an analytical electron microscope (AEM).
2. Description of the Prior Art
The ability to characterize materials by analytical electron microscopy is limited by the ability to detect and analyze constituents present in very small samples. Surface borne contaminants or surface films interacting with the high energy incident electron probe can create deposits on the surface of a sample interfering with the electron probe and thus adversely affect or prohibit accurate analysis.
Contaminants typically are introduced by one of four ways including the specimen, the specimen stage, carried into the chamber by the evacuation system, or are present on the internal components of the instrument. Contaminants from the evacuation system can usually be reduced by the manufacturer of the instrument, the first two items cannot.
The preparation of inorganic specimens (metals, ceramics, semiconductors, etc.) frequently involves chemical or electrochemical polishing, or ion milling followed by solvent rinsing and air drying. This typically leaves a residual contaminant or film on the specimen surface. Cleaning of specimen stage is also sometimes followed by rinsing of the stage with various organic solvents. Even though the organic solvents evaporate, a small amount of residue may typically remain on the sample and stage.
Also improper or poor techniques used to store both the specimens and/or stages prior to insertion into the microscope can introduce additional residues. While the majority of the films created in these processes dissipate, a small amount generally remains on surfaces and is sufficient to cause problems when the specimen is subsequently examined in modern analytical microscopes.
Although these residues are widely distributed and generally are at low concentrations on the various surfaces, some materials can become mobile in the microscope environment and are attracted to the periphery of any focused electron probe, forming deposits. Since these contaminants can travel large distances over the surface of a specimen, it is important to remove or immobilize these species as much as possible prior to an analysis without disturbing the microstructure of the specimen.
It has been well documented that low temperature (&lt;50.degree. C.) plasmas of various ionized gases can be used to reactively etch/ash organic materials found on the surface of materials. This has been used in the industrial community to clean semiconductor wafers and other bulk materials for many years. In that procedure, typically the material is placed in an RF cavity or a DC cavity with a flowing reactive gas. The nature of the gas selected is chosen based upon the desired effect. Oxygen or argon is generally used, however, specific gases (BCl.sub.3, CF.sub.4) may be used to tailor the reaction for the desired effect.
It is an object of the present invention to provide an improved method and apparatus for cleaning both a specimen stage and a specimen or any other item inserted into the vacuum system of an analytical electron microscope (AEM).
It is another object of the present invention to provide such an improved method and apparatus including a low temperature plasma.
It is another object of the present invention to provide such an improved method and apparatus including a low temperature reactive gas plasma that provides reliable and effective operation.
It is another object of the present invention to provide such an improved method and apparatus including a low temperature reactive gas plasma that overcomes many of the disadvantages of prior art arrangements.